"It's a nice sort of warm duvet of insulation for growing produce down there," Dring tells Morning Edition's Renee Montagne.

So how's it set up?

Here's how Dring describes it: "If you just imagine a bench with ... a mat on it, and then we just sew the seeds onto that mat. And then underneath the lights, the roots grow into the mat that's in the tray, and then every 12 hours, water waters the mat again, and under the light it grows, so no soil is required."

Sunlight, of course, doesn't reach that far underground. So Dring and Ballard use LED lights as a substitute. Dring says LED lights have evolved so much that you can pick and choose elements of the light spectrum to get light that's identical to the sun.

Those lights require energy, but to ensure the project truly is "zero carbon," the energy comes from a company that gets all of its energy from wind and solar.

As for what's under cultivation way down there, Dring says they've got arugula, lettuce and microherbs like coriander, mustard leaf and tatsoi.

One day, they might also grow tomatoes, which Dring assures would be very tasty, despite the fact that they're hydroponic.

Chef Roux's "palate is pretty damn good," says Dring. "Selling a homogenous, sort of tasteless tomato is certainly not part of our plans."

Besides a commitment to good flavor, Dring says he's hopeful the venture will succeed because it also can reach consumers far more quickly than vegetables grown on a farm outside London.

"Obviously as soon as you cut product, it starts to degrade in flavor," says Dring. "We can get it to the market in from field to fork, in four to eight hours. Usually it travels 72 hours, maybe four or five days. That's what's really interesting to our customers and wholesalers — that's what's turning them on."

Copyright 2014 NPR.

Michel RouxMichel Roux

Old London Air Raid Shelter Becomes Vegetable Farm